1. Field of the Invention
The present disclosure relates to light emitting devices that can be used for light emitting diodes (LEDs) and laser diodes (LDs). More particularly, the present disclosure relates to a light emitting device that includes at least one carrier trap portion in at least one layer within a multi-quantum well structure.
2. Discussion of the Background
Group-III nitrides, such as GaN, AlN, InGaN, and the like, have good thermal stability and direct transition type energy-band structure, and have received attention in recent years as materials for blue and UV light emitting diodes and laser diodes. Particularly, InGaN compound semiconductors are attracting attention for their narrow band-gap energy. LEDs employing GaN-based compound semiconductors have various applications including full color flat panel displays, light sources of backlight units, signal lamps, interior lighting, high-definition light sources, high-resolution output systems, optical communications, and the like.
Generally, the LED includes an n-type semiconductor layer, a p-type semiconductor layer, and an active region interposed between the n-type and p-type semiconductor layers. The n-type and p-type semiconductor layers may be formed of Group-III nitride semiconductor layers, for example, (Al, In, Ga)N-based compound semiconductor layers. The active region may have a single quantum well structure having a single well layer or a multi-quantum well structure having multiple wells and barrier layers. The multi-quantum well structure may include InGaN-well layers and GaN-barrier layers alternately stacked on top of each other. The InGaN-well layer may be formed of n-type or p-type semiconductor layer, which has a smaller band gap than the barrier layer, so that a quantum well layer can be formed to permit recombination of an electron and a hole therein.
The Group-III nitride semiconductor layer is grown on a heterogeneous substrate having a hexagonal structure, such as a sapphire substrate or a silicon carbide substrate, via metal organic chemical vapor deposition and the like. However, when the Group-III nitride semiconductor layer is grown on the heterogeneous substrate, the semiconductor layer undergoes cracking or warpage and dislocations due to differences in lattice constant and thermal expansion is coefficient between the semiconductor layer and the substrate.
To prevent such problems, a buffer layer is formed on the substrate before growing the semiconductor layer, so that crystal defects can be substantially prevented in the semiconductor layer grown on the buffer layer. Nevertheless, the active layer still has a high density of crystal defects, thereby providing a severe obstruction in application of the Group-III nitride semiconductor layer. Further, the crystal defects such as dislocations in the active region trap carriers introduced into the active region and do not emit light, thereby acting as a non-radiative center and significantly deteriorating internal quantum efficiency of the LED.